Bombsight



March 15, 1955 c. L. NORDEN 2,703,932

' BOMBSIGHT Filed Jan. 25, 1945 5 Sheets-Sheet 3 INVENTOR CARL L NORDE N ATTORNEY C. L. NORDEN BOMBSIGHT 5 Sheets-Sheet 4 II\/;NVENTOR CARL L. NQRDEN ATTORNEY March 15, 1955* Filed Jan. 25, 1945 March 15, .1955

Filed Jan. 25, 1945 c. L. NORDEN 2,703,932

BOMBSIGHT 5 Sheets-Sheet 5 PI (I030) INVENTOR CARL L. NORDEN BY W ATTORNEY BOMBSIGHT Carl L. Norden, New York, N. Y., assiguor to the United States of America as represented by the Secretary of the Navy Application January 25, 1945, Serial No. 574,593

13 Claims. (Cl. 33-465) This invention relates to bombsights of the synchronizing typ c in which the speed of a driving member is varied in accordance with the bombing altitude to place the sight in proper condition for operation at that altitude. More particularly, the invention relates to a novel device for automatically controlling the speed of the driving member of a synchronizing bombsight to extend the range of conditions under which the sight may be used with accuracy to include climbs and glides as well as horizontal flight of the aircraft.

Bombsights of the synchronizing type are well known in the art, a bombsight of this type being disclosed in a copending application of T. H. Barth, Serial No. 635,298, filed Sept. 28, 1932, which matured into Patent 2,438,532. In such bombsights, the solution of the dropping angle of the bombing problem involves manual adjustment of a variable speed driving connection between a constant speed driving member, or speed disc, and a movable optical element of a stabilized sight on the aircraft, to synchronize the movement of the optical element in conformity with the apparent movement of the target as seen through the sight, whereby the sight is kept trained upon the target during the bombing run. This manual adjustment of the speed of movement of the optical element automatically operates a computer which solves for the proper dropping angle to cause the bomb to hit the target. When the sighting angle to the target corresponds to the dropping angle thus solved, the bomb is released.

In prior bombsights of the synchronizing type, it has been necessary for the bombardier not only to adjust the variable speed driving connection to maintain the synchronism referred to, but also to adjust the speed of the constant speed driving member, hereinafter referred to as the speed disc, in accordance with the predetermined altitude of the bombing run, thereby setting into the bombsight an altitude factor upon which successful solution of the bombing problem depends. Accordingly, any error in the bombardiers speed setting of the speed disc, or any non-conformity between such speed setting and the bombing altitude of the aircraft, will reflect upon the accuracy of the bombing results. Moreover, with such a bombsight, it is diflicult if not impracticable to make a bombing run during gliding or climbing of the aircraft, since it would then be necessary for the bombardier to make continual speed adjustments of the speed disc with the changes in altitude, in addition to the synchronizing adjustments of the variable speed driving connection and the usual adjustments to set up a collision course with the target.

An object of the present invention, therefore, resides in the provision of a bombsight of the synchronizing type in which the possibility of introducing errors through faulty speed adjustment of the speed disc in accordance with the bombing altitude is materially reduced.

Another object of the invention is to provide a bombsight of the character described in which the driving speed of the speed disc is automatically controlled in accordance with changes in altitude, whereby the range of conditions under which the bombsight may be used with accuracy is extended to include climbs and glides, as well as horizontal flight.

Still another object is to provide in a synchronizing bombsight of the character described, a control device responsive to altitude and to rate of change in altitude for automatically introducing into the movement of 2,703,932 Patented Mar. 15, 1955 'ice the bombsight mechanism the necessary corrections to provide for nonhorizontal bombing.

A further object is to provide in a synchronizing bombsight of the character described, a control device for automatically calculating the major portion of the disc speed so that the correction put in by the bombardier is not critical as regards altitude, and he can make all settings well in advance of the bombing run without loss of accuracy.

Still another object of the invention is to provide a synchronizing bombsight control for the speed disc, including means for measuring the altitude H and the vertical velocity Vrr of the aircraft, and a computer which receives the H and Vn values from the measuring means, together with a ballistic correction put in by the bomhardicr, and computes the disc speed for the bombsight, whereby the bombsight may be used with facility and accuracy [or climbing or gliding runs.

An additional object is to provide a control for synchronizing bombsights of the character described, which automatically maintains the speed disc at a speed proportional to where tv is the time of flight in vacuo of a bomb released from the plane at any distant, and H is the altitude of the plane above the target at that instant.

Another object resides in the provision of a synchronizing bombsight control having a computer mechanism comprising means responsive to displacements expressing altitude and rate of change of altitude of the aircraft, and means operable thereby for transforming the displacements into a corresponding rotational speed of the bombsight speed disc.

A further object is to provide a synchronizing bombsight attachment for automatically controlling the speed of the bombsight speed disc, which comprises a computer operable by an altimeter to apply altitude and vertical velocity corrcctions'nto the speed disc, based upon vacuum conditions, and a single manual adjustment for correcting the speed disc for all other factors, including the corrections necessary to reflect actual ballistic conditions and also the corrections necessary in view of the use of the usual bombsight trail setting for horizontal flight.

Still another object is to provide a control device 0 the character described which includes safety means for automatically cutting out the altitude control when the altitude passes beyond preset limits, thereby preventing possible damage to the device.

Another object is to provide a control device of the character described having safety means for automatically cutting out the vertical velocity control when such velocity exceeds preset limits, thereby preventing possible damage to the device.

These and other objects of the invention may be better understood by reference to the accompanying drawings, in which:

Figs. 1 and 1A are schematic views of; one form of the new control showing, respectively, the barometric means for providing displacements expressing altitude and rate of change of altitude, and the computer mcchantsut for trnnsloruuu the. displacements into a corresponding rotational speed of the bombsight speed (1150,

it being understood that the computer is connected to the barometric means along the lines /\-A in Figs. 1 and 1A;

Fig. 2 is a schematic wiring diagram showing the electrical circuits of the control;

Figs. 3 and 4 are schematic views of a typical synchronizing bombsight mechanism with which the new control 'may be used, and

Figs. 5 and 6 are vector diagrams illustrating the operation of the main and secondary parts, respectively, of the computer.

The control device of the present invention, as illustrated, is in a form suitable for use with a synchronizing bombsight such as that disclosed in the copending application of T. H. Barth, Ser. No. 635,298, filed September 28, 1932. However, it is to be understood that the invention may be used with other forms of synchronizing bombsights, wherein the solution of the bombing problem depends upon maintaining the speed disc, or other driving element, at a speed which is a function of the bombing altitude of the aircrzni.

In order to comprehend more rapidly the operation and purpose of the new control. a typical synchronizing bombsight mechanism will be described, it being understood that all bombsights in general perform two functions, as follows: (1) They enable the pilot to guide the aircraft on a collision course so that the aircrafts track passes in the proper position with respect to the target to cause the bomb, when released, to hit the target in deflection; and (2) they calculate the proper point of release of the bomb so that it will have the correct range to hit the target.

Synchronizing [mm/might The synchronizing" bombsight is so-called because in its performance of the second function noted above. a movable element of the target sighting sysem or telescope is driven slowly about a pitch (lateral) axis on the aircraft at the proper speed, determined by manual speed adjustments, to cause the point of aim through the telescope to remain on the target and follow the apparent target motion during the bombing run, these speed adjustments being used in the solution of the range part of the bombing problem, that is, the dropping angle. In solving for the dropping angle, the bombsight employs the values of the known time of ilight of the bomb, it (which is determined for a bomb with a given ballistic coefiicient from the altitude (H) and air speed of the aicrcraft), the speed of approaching or closing the target along the ground at the instant of bomb release, V (which is computed in the bombsight with the use of its optical system), and the known trail factor. 'I (which is determined for a bomb having a given ballistic cocflicicnt from the altitude (H) and the air speed of the aircraft). The bombsight solves the right triangle having the altitude (H) as one side, the horizontal bomb range (Vc[/--T) as the other side, and the slant range as the hypotenuse, for the dropping angle The bomb is released when the optical or telescope axis on the target is at an angle to the vertical equal to the dropping angle, that is,

A synchronizing mechanism for solving this triangle is illustrated schematically in Figs. 3 and 4. As there shown, the mechanism comprises a driving member or speed disc 5 and a driven roller 5a engaging one face of the disc and journallcd' iii'a carriage 5!) threaded on a vertical screw spindle 5c. The spindle 5c is slidable vertically in a hearing 50? and is also rotatable by a rate knob 50 so as to raise or lower the carriage, which is held against rotation by a suitable guide, thereby moving the roller 50 radially with respect to the axis of rotation of speed disc 5. It will be apparent that the mechanism described provides a variable speed drive in which the speed of the driven roller 5a depends upon the radial distance of the roller from the axis of the driving disc 5, as determined by the adjustment of rate knob 5a.

The roller So has a pinion 5f meshing with a gear 5g which drives one end of a differential 5/2. the other end of the ditl'crcntial being adjustable by a displacement knob 5i through a clutch 51'. The output end of the differential 5/1 is connected through a shaft 5k and a pinion 5m to a rack 6 having a stud 6n engaged in an elongated slot 61) in a sector plate 6('. The sector plate is rotatable on an axis 6d, the slot 611 being disposed radially with respect to the axis.

The bearing 5:! surrounding the spindle 5c is provided with an externally threaded portion for receiving a nut gear 7. A thrust washer 7a is supported on the nut gear, the washer in turn supporting a pinion 511 on the upper end portion of spindle Sc so that the spindle and its carriage 5b are carried by the nut gear. The nut gear 7 meshes with a gear 71 mounted on the lower end of a shaft 7c which is rotatable in a sleeve 7(/ having an external flange resting on part of the bombsight housing B. The shaft 70 is rotatable by a trail arm 70 having a pointer 71 cooperating with a trail scale 7g. By swinging the trail arm 72, the spindle 5c may be raised or lowered through the nut gear 7, so as to adjust the roller position on speed disc 5 without rotating the spindle.

The pinion 5n on the screw spindle meshs with a rack 8 mounted for longitudinal movement in parallel spaced relation to the rack 6, the two racks 6 and 8 being disposed on opposite sides of the axis 611. The rack 8 has a stud 8n engaged in a slot 8!) in a rate arm 80 rotatable about the axis 6d, the rate arm having at its free end an arcuate portion 8d carrying a pivoted release finger 8c. The finger 8c is spring-pressed against the periphery of sector plate 60, which has a notch 60 so positioned that the finger is adapted to enter the notch when the slots 6.) and 8b are on a common diameter through the axis 6d. Rotation of the spindle 5c by rate knob 52 adjusts the roller 5a radially with respect to the axis of speed disc 5 and, at the same time, drives the rate rack 8 through pinion 511 so as to swing the rate arm 8c from the vertical by the action of stud 8a in slot 811.

In the bombsight mechanism as described. a small right triangle is formed in which the hypotenuse is reprcscntcd b a line from axis (HI along arm tie to stud tin on rat-it 8, uhttcbnc side th) is represented by a line from the rack 8 to axis (n1 and pcrpcmticular to the rack. and the other side is represented by a line along rack 8 from the vertical line (It) to the stud 8a. A second right triangle is also formed in which the hypotenuse is represented by a line from axis 6:! along slot 6b to stud 6n, while one side (It) is represented by a line from rack 6 to axis 6d and perpendicular to the rack, and the other side (1') is represcntcd by a line along rack 6 from the vertical line (It) to the stud 6a. This second triangle is similar to the triangle formed in space by the aircraft's altitude or vertical to the aircraft (H), the distance along the ground from the foot of this vertical to the target, and the line of sight between the aircraft and the target, whereby the second triangle in the bombsight mechanism has in it anangle (y) equal to the sight or range angle to the target.

The bombsight also includes an optical sighting system, preferably in the form of a telescope T. which is stabilized in both vertical and horizontal planes by gyroscopic means (not shown). in practice, the telescope is mounted at a point remote from the sector plate (it: and includes a mirror operatively connected to the sector plate and movable thcreby about a pitch (lateral) axis, whereby rotation of the sector plate through roller 5a and rack 6 causes a corresponding movement of the telescope linc-of-sight about the pitch axis. Accordingly, for illustrative purposes the synchronizing mcchanism may be considered as stabilized in horizontal and vertical planes and supporting the telescope on the sector plate 60 with the telescope axis coinciding with the axis of slot 6!). It will be apparent that the telescope T may be adjusted about the pitch axis 6d independently of roller 511 by means of the displacement knob 51. By adjusting the angle of slot 6b (and therefore the telescope) through displacement knob 5i and adjusting screw spindle 5c from rate knob 5c. the bombardier can place the horizontal reference line of the telescope on the target and cause this line to move in synchronism with the target, and when the telescope sight angle (y) equals the dropping angle (0) as set into the first triangle by rotation of arm 80, the finger 8c enters notch 6e and actuates suitable means (not shown) for releasin the bomb.

In practice, the two sides of the right triangle having the dropping angle (0) equal to is set into the bombsight is as follows: As the trail (T) is set by adjustment of arm 70, the roller 5a is displaced above the axis of speed disc 5 a distance proportional to the trail, without turning the screw spindle 5c. Displacement knob 51' is operated to adjust the sight angle (y) so that the telescope line-of-sight is on the target. Then, as

1 from arm 7e.

the bombardier turns the spindle So from rate knob 51: to cause the telescope line-of-sight to move along the ground at the same rate as the target, for synchronism, the roller 5a is moved farther above the speed disc axis until the roller distance is sutficient to give the desired synchronism. In turning the spindle 5c, the rate arm 80 is rotated to a position so that the distance of stud 80 from the vertical (h) is proportional to the amount the rate knob 5c is turned. In other words, the roller displacement from the speed disc axis is proportional to However, not all of this roller displacement is due to rotation of spindle 5c through the rate knob 5e, since part of the displacement was due to setting in the trail factor (T) The remainder of the roller displacement, as set in by the rate knob Se is proportional to (Van) T H 'lherel'ore. when the sight is properly synchronized. the

tan

Thus, when the sight angle (y) to the target, as represented by the angle of the common axes of telescope T and slot 611 to the vertical (h), equals this dropping angle so that the bomb is released due to engagement of finger 8c in notch 62, the bomb should have the proper range to hit the target.

In prior synchronizing bombsights. the speed disk is driven by a constant speed motor having a manual speed adjustment (not shown) which is operated by the bombardier to set in a predetermined disk speed. That is, prior to the bombing run, the bombardier determines the altitude and the air speed at which the run is to be made and, from a bombing table, obtains the proper disk speed corresponding to these values. The accuracy of the bombing results. therefore, will be affected adversely to a substantial degree by any error of the bombardier in ascertaining the altitude, determining the corresponding disk speed from the chart, or setting the disk speed into the disk 5. Moreover. such bombsights are generally limited to horizontal bombing, because changes in altitude during the bombing rim would require continual manual adjustments of the speed of disk 5, and it is impracticable for the bombardier to make such adjustments while maintaining synchronism through adjustment of rate knob 50.

Automatic disk speed control According to the present invention, I provide a device for automatically controlling the speed of disk 5 in accordance with the instantaneous altitude and rate of change 4 SmkgZ-As n. I. M.

where k tne sight constant (for example, 5300).

g=the acceleration of gravity=32.l6 l.t./sec.

Iv=ih6 vacuum time of flight in seconds of a bomb released from the plane at any instant.

H=the altitude in feet of the plane above the target.

Vr1=the rate of descent of the plane in feet per second.

aSzza correction for the ballistic coefiicient of the bomb and the approximate release conditions.

The first term of l) and (2) is computed automatically from measured values of the altitude H and the vertical speed VH, while the correction AS is obtained from tables and put in manually by the bombardier. The trail setting (arm 7e), which is made in the normal manner, is obtained front tables and is the same for glide and climb bombing as for horizontal bombing at the same air speed and release altitude.

As illustrated, the new control device is in the form of an auxiliary instrument which may be attached to the housing B of the synchronizing bombsight. The attachment comprises a barometric system for measuring the altitude H and the vertical velocity Va, and a computer which receives the H and V}; values from the barometric system, together with a ballistic correction put in by the bombardier, and computes the disk speed for disk 5, the output end of the computer being connected directly to the disk.

The barometric ystern The barometric system measures atmospheric pressure by balancing the force of the pressure on two partially evacuated bellows against two balanced springs. so that the extension of the bellows remains substantially constant. The bellows, shown at l0 and lthi, are of the sylplion type and are supported in opposed relation on mounts ll in an airtight casing (not shown) with the axes of the bellows parallel and slightly spaced. A strap 12 is secured at its ends to the free ends of the bellows and loops through a slot in a rotatable shaft 3 mounted midway between the two bellows. The shaft 13 is rotated so that the bellows are extended and partially evacuated, whereby the atmospheric pressure on the bellows exerts a torque on the shaft. This torque is balanced by two balance springs 14 and 14:: arranged parallel to the bellows and fastened to the ends of lever arms 15 on the shaft. The ends of springs 14, 141: remote from their respective lever arms 15 are connected to racks l6 and 16:: through adjustable connections 17 and 17a, rcspcctively. A pinion 18 on a shaft 18a is disposed between the racks and in mesh with the rack teeth, so that clockwise rotation of the pinion acts through the racks to extend the springs. while counterclockwise rotation of the pinion acts through the racks to relieve the tension in the springs.

A second arm 20 on shaft 13 is operutively connected at one end to a contact lever 21 pivoted intermediate its ends on a fixed mounting 22 which is grounded, as shown at 22a. The movement of arm 20, and therefore shaft 13, is limited by suitable stop means 23 on a mount 11a in the casing adjacent the opposite end of the arm. In the nor mal position of lever 2|. its end remote from arm 20 is positioncd between and disengaged front two fixed contacts 24 and 24a mounted on an insulated support 25. If the atmospheric pressure increases from a constant value, the torque of the bellows 10, 1011. becomes momentarily stronger than that of springs 14, 1411 so that the shaft 13 rotates counterclockwise slightly. This causes arm 21 to engage fixed contact 24 and operate a servomcchanism (which will be described presently) to drive pinion 18 in the opposite direction, thereby extending the springs 14, 141! through the racks and returning arm 21 to its neutral position. Conversely, a decrease in atmospheric pressure causes the torque of springs 14, 14a to become momentarily stronger than that of the bellows and move shaft 13 slightly clockwise, whereby contact arm 21 engages the other fixed contact 24 to rotate pinion 18 counterclockwise through the servomcchanism and thus reduce the spring extension and restore the parts to their neutral positions. Accordingly, the angular position of shaft 13 is held constant within very close limits. Since the force on bellows 10, 1011 is proportional to the at mosphcric pressure, and the force of springs l4, Mn is proportional to their extension, it follows that the angrilar position of pinion I8 is a measure of the atmospheric pressure, and its angular speed is proportional to the rate of change of atmospheric pressure.

The bellows, springs, gear racks, pinion and contacts are sealed in an airtight casing (not shown) having a connection leading to a litot static line, so that the atmospheric pressure which is measured by the barometric element is the air pressure outside the aircraft, rather than the pressure within the aircraft. The shaft 180, through which the pinion 18 is driven by the servomechanism, extends through a wall of the casing.

The fixed contacts 24 and 24a are connected through wires 27 and 27a to electromagnets 28 and 2811, respectively, ,for controlling the servomechanism. The electromagnets are connected through a common conductor 29 to the positive side of a current source 30, the negative side of which is grounded, as shown at 30a.

Clappers 31 and 31a operable by the respective magnets 28 and 28a operate against springs, not shown, to engage clutches 32 and 32a on gears 33 and 330, respectively. The gears 33 and 331: mesh with a common gear 34 and are adapted to be clutched to oppositely rota ing gears 35 and 350, respectively, through operation of the respective clappcrs 31, 31a by electromagnets 28, 28:1. Tints, when the clcctromagnet 28 is energized by engagement of arm 21 with contact 24, as described, the gears 33 and 35 are clutched together to drive gear 34 in one direction, while energizing of electromagnet 281/ by engagement of arm 21 with contact 240 causes gears 33:: and 35a to be clutched so as to drive gear 34 in the opposite direction.

The gears 35 and 35!: are driven by a constant speed motor 37 having a suitable speed regulator 38 and a drive shaft 39. A pinion 40 on the shaft 39 drives disk 41 attached to a shaft 42 and having a friction face upon which a roller 43 rides. The friction disk 41 is urged into a driving engagement with the periphery of roller 43 by means of a compression spring 44 seated at one end on a shoulder 42 on shaft 42 and at the other end on the bottom of a cup-shaped spring housing 45 which' guides the shaft 42. A gear 46 on shaft 42 meshes with and drives the gear 35a which, in turn, meshes with and drives gear 35 in the opposite direction.

The driven gear 34 is connected through a shaft 48 and bevel gearing 49 to a spindle 50 having a thread course 51 threaded into a carriage 52 on which roller 43 is mounted for rotation. The carriage 52 is held against rotation by suitable guide means (not shown) so that rotation of spindle 50 causes its threaded portion 51 to slide the carriage 52 lengthwise of the spindle and thereby move roller 43 across the face of friction disk 41 in a radial direction with respect to shaft 42. The roller 43 is rotatable on an axis parallel to spindle 50 and has an elongated pinion 53 meshing with a gear 54 connected to one side of a differential 55 which is driven in one di' reetion by gear 54 at a speed proportional to the distance of roller 43 from the center or axis of rotation of friction disk 41. The other side of the differential 55 is driven in the opposite direction at constant speed from gear 46 through a gear 56. a worm 57 and a worm wheel 58. Thus, the output of differential 55 will be zero when roller 43 is displaced from the axis of disk 41 to a neutral" position such that the speed which it imparts to the differential through gear 54 is equal to the constant speed itnpartcd to the differential through worm wheel 58. In other words, the output speed of differential 55 is proportional to the distance of roller 43 from this neutral" position offset from the axis of rotation of friction disk 41-: The purpose of differential 55 is to avoid wear between roller 43 and disk 41 by keeping the roller away from the center of the disk when the altitude is constant.

The output of differential 55. through gears 59 and 60. drives one side of a second differential 61, the other side of which is driven in the same direction from spindle 50 through gears 62, 63, 64, and during acceleration. The gear 65 is also connected through a gear 66 to a drum 67 having 21 V11 scale graduated in feet per second. At its output end, the differential 61 is connected through a shaft 70 and bevel gearing 71 to an altitude cam gear 72 rotatably mounted on a shaft 73. An altitude scale 74 on the altitude gear 72 cooperates with a stationary \ointer 74d to indicate the altitude as measured by the uuotnttric means including the bellows and springs 10. ltlu, l4, I411. The altitude gear 72 has a cam 75 engaging a follower 76 on a rack 77 provided with an clongated guide slot through which shaft 73 extends. The rack 77 meshes with a pinion 78 mounted on shaft 18:! and operable to drive the pinion 18.

It will be apparent that the cam gear 72 is driven through the servomechanism described at a speed proportional to the distance of roller 43 from its neutral" position, plus an additional constant amount through gearing 6265 only while the roller position is changing due to rotation of spindle 50. This additional speed hastens the correct positioning of the altitude gear 72 through the output of the second differential 61. The amount by which roller 43 is displaced from its neutral position on disk 41 in order to maintain the correct speed of altitude gear 72 is proportional to Va and is indicated on the Via scale 67 through spindle 50 and gearing 62-66. The shape at that instant.

8. of cam 75 is based upon the pressure-altitude relation of the standard atmosphere, so that for a given pressure change (angular change of pinion 18) the resulting rotation of cam gear 72 through the servomechanism is proportional to the corresponding change in pressure altitude. Thus, the position altitude gear 72 is an indication of the pressure altitude, H, and its speed of rotation is a measure of the rate of change of altitude. Vn.

The spindle 50 is provided with a pinion 80 connected through bevel gearing 81, shaft 82, pinion 83 and gear 84 to a V1; shaft 841:. Similarly, the beveled gearing 71 is connected through gear 85 to an H shaft 86.

The operation of the barometric element is as follows: Assume that the aircraft starts a climb from level flight, accelerating for a short time and then maintaining a steady rate of climb. As the altitude increases. the pressure in the casing containing the bellows 10. 10.1 dccreases, the torque of the bellows becomes less than that o esprings 14. 14a. and the climb contact 24 is engaged by grounded contact arm 21 so as to energire magnet 28. As a result, spindle 50 is connected to constant speed gear 35 through the magnet operated clutch 32 and gearing 33, 34 and 49, the resulting rotation of the spindle mov ing the roller 43 toward the center of disk 41 and away from its neutral" position. The altitude gear 72 and cam 75 are thus rotated in a direction of higher altitude by the constant speed input to the second differential 61 through spindle 50 and gearing 6265. plus the variable speed input to-differential 6| arising frotn the displacement of roller 43 from neutral." As soon as the altitude cam 75 has rotated by an amount equivalent to the change of altitude. the contact 24 is disengaged by the action of the cam 75 through rack 77, pinions 78 and 18, racks 16. 16a and springs 14, 14a, whereby the constant speed input to the second differential 61 from gearing 62 65 is stopped. However, since the roller 43 is still displaced from its "neutral position. the altitude cam 75 continues to rotate at a speed proportional to this displacement. ll the aircraft is still accelerating in its climb, the speed at which pinion 18 is driven by altitude cam 75 will not be sufficient to decrease the torque of springs 14, 1411 at the same rate as the torque of bellows 10. 10a is decreasing due to the accelerating climb, so that contact 24 will be engaged again and the operation repeated, causing further displacement of roller 43 from neutral. Actually, the response sensitivity of the barometric system is such that with climbs at usual accelerations. the contact arm 21 flutters between its neutral position and contact 24, the proportion of the time that contact 24 is engaged being larger with higher accelerations. Thus. during an accelerating climb the roller 43 is displaced from neutraf by a rapid suucession of small increments which vary in magnitude and frequency with the rate of acceleration, it being understood that the roller acceleration due to its displacement by spindle 50 is substantially in excess of the maximum climb (or glide) acceleration of the aircraft. Accordingly, while the roller displacement rate during each displacement increment is' constant (because of the constant speed of spindle 50), the average rate of the displacement due to a succession of these increments is proportional to the acceleration rate of the climb (or glide), and the roller displacement from ncutral" at any instant may be considered equivalent to the climb rate When the aircraft reaches a steady rate of climb with the roller 43' in lhe exact position on disc 41 equivalent to this rate. contact arm 21 discngugcs contact 24 and remains in the neutral position, the altitude cam 75 driving pinion l8 counterclockwise at a speed proportional to the rate of climb so as to maintain a balance between the decrasing torque of springs 14, 14a and bellows 10, 1011.

When the rate of climb dcercascs. the pinion 13 is driven counterclockwise at a speed which momentarily causes the torque of springs 14, 14a to decrease more rapidly than the torque of the bellows. whereby the bellows torque will predominate and cause contact arm 21 to engage the other contact 24a and operate clutch 32:1. Spindle 50 will then be rotated in the opposite direction so as to move roller 43 back toward its "neutral" position. However, during this return movement of the roller, the roller and the altitude cam 75 will continue to rotate in the same direction as in the accelerating climb, since the roller is still displaced on the climb side of its neutral position. Thus, the altitude cam 75 will cause a fluttering action of contact arm 21 between its neutral position and the fixed contact 240, and the return movement of the roller will take place in a rapid succession of small increments as previously described in connection with the accelerating climb, except that the increments will be in the opposite direction. When the aircraft again attains level [light so that the climb rate is zero, the roller 43 is moved to its neutral" position, the altitude gear 72 is stopped in the position corresponding to the new constant altitude, and the contact arm 21 is maintained in neutral between fixed contacts 24 and 24a.

In a glide, the operation is the same except that the contact 2411 and clutch 32a are engaged during acceleration of the glide, and the contact 24 and clutch 32 are engaged during deceleration of the glide.

Computer The computer comprises two disks 90 and 90a mounted in parallel spaced relation and rotatable on coaxial shafts 91 and 9111, respectively. The disks are driven in opposite directions at constant speed by the motor 37 through shaft 39 and gears 92, 92a and 93. A roller 94 is mounted between the disks 90, 90a and is rotatable in a cage 95 which is adjustable to move the roller radially with respect to the disk axes. The cage 95 is adjusted to position the roller by combinations of H, VH and a manual setting, so that the roller is driven by disks and 900 at a speed equal to leg t, a 17" The roller 94 has an elongated pinion 96 meshing with a gear 97 which is connected through a shaft 971: and a tlexible drive shaft )8 to bcvcl gearing 99 which. in turn, is connected to the speed disk of the synchronizing bombsight. As shown, the bevel gearing 99 is mounted in a casing 100 extending from the bombsight housing it. The main computer comprises a right-angle lever 102 having elongated slots 102a and 1021) in its respective arms, the lever being pivoted to a main computer slide 103 by a stud 104 at the point of intersection of the axes of slots 102a and 102/). A fixed stud 105 fits into the slot 102a, while a V}! rack stud 106 is engaged in the other slot 102]). The Vn rack stud 106 is secured to a Vrr computer slide 107 which is movable parallel to the direction of motion of the main slide 103 (vertically as shown and as the instrument is mounted) by an elongated Vii pinion 108 on the Vrr shaft 84a, the pinion 108 meshing with a rack 107a on slide 107. The slide 107 is carried by and slidable on a computer block 110 movable longitudinally on a threaded H spindle 111 which is connected through gears 112 and 112a to the H shaft 86. The motion of block 110, due to rotation of threaded H spindle 111, is perpendicular to the direction of motion of slide 107 and in a direction away from stud 104 as the altitude increases. The V}; slide 107 is driven upward by shaft 84a in response to glide acceleration or climb deceleration.

The displacement of slide 103 from its zero or reference position is proportional to as will be described presently. This displacement can be zero only if H equals zero, that is, if stud 106 coincides with stud 104. This is obviously impossible, and in order to prevent jamming as the altitude approaches zero, the slot 102/) for stud 106 is curved at 1020 toward the other slot 102:: as it approaches the slide stud 104. As a result, the motion of slide 103 is no longer proportional to after the pin 106 passes into the curved portion of its slot. The parts may be adjusted so that this action occurs at a lower limit of operation, for example, 4,000 feet for V1; equals zero and at somewhat higher altitudes for larger values of Vr-r.

The operation of the main computer is illustrated in the vector diagram of Fig. 5. Referring to Fig. 5:

A is the position of right angle lever fixed stud 105 P is the position of stud 104 C is the position of the VH rack stud 106 O is the zero position of stud 104 vmraar=vn+gt Since the required speed of disk 5 is proportional to it is necessary to obtain motion inversely proportional to that of the main computer slide 103. Accordingly, a sccondary computer is provided which comprises u secondary computer lcvcr 114 pivoted on a tixcd base. as at 115. and having two parallel slots 114a and 1141) in opposite sides of the lover. The slot 114:: receives and is guided by a pin 103 on the lower end portion of slide 10.1, while the other slot [141 receives a guide pin 116 on a secondary computer slide 117, which moves at right angles to the main computer slide 103. The operation ol. this secondary computer is illustrated in the vector diagram of Fig. 6. Referring to Fig. 6: O=pivot point 115 PI -POSlII OH of pin 103a Pz:position of pin 116 OM rlt distance from pivot 115 to axis of slide 103 NP2=d2=distancc from pivot 115 to axis of slide 117 A IPI SX- dlSPIHCCITlCIlt of slide 103 MP1=:OP of Fig. 5 ON=S2=displacement of slide 117 From similar triangles dis. ar?

The displacement of slide 117 from its zero position is therefore proportional to A right-angle crank 119 is pivotally mounted at 120 on the secondary computer slide 117, and the vertical arm of lever 119 is connected through an adjustable connection 121 to the roller cage 95. The horizontal arm of the right-angle lever 119 has a pin 122 which rides in a channel 123 in a cross member 123, the channel being parallel to the axis of slide 117. The cross member 123 is mounted on the lower end portion of a disk speed correction slide 124 having a vertical slot for receiving a guide pin 125. The slide 124 is adjustable vertically by a disk speed correction knob 126 rotatably mounted on the fixed base (not shown) and having a shaft 127 threaded into the upper end portion of slide 124. A pointer 126a cooperates with a suitable scale on the knob 126. The member 124 is also guided vertically by memher 128.

It will be apparent that any vertical motion of the disk speed correction slide 124, by adjustment of knob 126, moves the lever 119 on pivot 120 and thus operates through connection 121 to position the roller 94 relative to the secondary computer slide 117. The displacement of roller 94, and therefore the roller speed, is made up of two parts, namely, the displacement of the secondary computer slide 117 which is proportional to and a constant amount proportional to the setting of the disc speed correction knob 126. The constants of the instrument are so chosen that the speed of the output shaft 970, and therefore the speed disc of the synchronizing bombsight, in R. P. M., is

kg 6,, S- 2 X AS where k is the bombsight constant (for example, 5300) and AS is the reading of the disc speed correction dial 126.

A gear 130 is fixed to the gear 112-on H spindle 111. the gear 130 being connected through gearing 132 and 133 to a shaft 134 having a worm 135 which drives a worm wheel 136. The wheel 136 is rotatable on a shaft 136a and has an altitude scale 136c cooperating with a fixed pointer 13617. A vernier wheel 137 is driven directly by shaft 134 and has an altitude scale cooperating with a fixed pointer 1370. Since the barometric system of the present device. like any standard altimeter, measures pressure altitude, it is necessary to make corrections to the altitude factor put into the computer (by H shaft 86) for variations from standard atmospheric conditions This is done by sliding the gears 112, 130 to the right ou of engagement with gear 112a, so as to disengage the gear 112 from the barometric system, and by turning the spindle 111 independently to change the altitude setting on the computer and the scale 1364.- by the amount of the required correction. For this purpose, the gears 112 and .130 are mounted on a sleeve 138 splincd to and slidable on the H spindle 111, the gear 112 being normally urged into mesh with gear 11211 by a compression spring 139 coiled around the sleeve 138 and seated between the gear 130 and lixcd abutment 13811. An altitude setting knob 140 connected to sleeve 138 serves to disengage the gears 112 and 1121! and also to rotate H spindle 111 and thereby adjust the computer and altitude scale 1360, as described.

Limit switches The circuits between the barometric contacts 24, 24a arid the control electromagnets 28, 28a of the servo mechanism includes a transfer limit swltch 142 (Fig. 2). The switch 142 comprises flexible switch arms 143 and 144 in series with climb conductor 27, the arms normally maintaining their coacting contacts closed. Similarly, the glide conductor 2711 leads through normally engaged switch arms..-143a and 1440. The switch arms 144 and 144a are connected to adjacent contacts 145 and 1450, respectively, between the two sets of switch arms. An insulated sector plate 146 is loosely mounted on the pressure altitude cam shaft 73 and has lugs 147 and 147a disposed between and normally engaging extensions of the outer switch arms 143 and 143a, respectively. Due to their inherent spring tension, the arms 143 and 14311 normally hold the plate 146 in a centered position between the arms, as shown. Intermediate the lugs 147 and 1470, the plate 146 is provided with contacts 148 and 14811 which are normally spaced outwardly from the contacts 145 and 1450, respectively, and are grounded, as shown at 14). A pin .150 on the plate 146 is engageable by an arm 151 mounted on and rotatable with the shaft 73.

If the pressure altitude should increase above a predetermined limit, for example 20,000 feet, the resulting counterclockwise movement of altitude cam shaft 73 (Fig. 2) c.tus.s arm 151 to engage pin 150 and moves sector plate 146 slightly in a counterclockwise direction. Accordingly, the lug 147 opens the switch 143, 144 so as to break the circuit through climb conductor 27 to the scrvomechanism. Thus, the climb clutch 32 is disengaged to prevent further displacement of roller 43 from its neutral" position on disc 41, the roller and pressure altitude shaft 73 continuing to rotate, however, in the same direction at the speed corresponding to the roller displacement. Further counterclockwise movement of sector plate 146 causes contact 148a to engage contact 1451:, so that a circuit is established from the positive side of current source 30 through conductor 29, glide magnet 28a, conductor 27a, arm 144a, contacts 145a and 148a, and ground connections 149 and 30a to the negative side of the current source. Thus, the glide clutch 32a is til) tion until arm 151 again moves sector plate 146 counterclockwise to open the climb switch 143. 144 and close glide switch a, 1480. This operation is repeated until the pressure altitude decreases below the selected upper limit, whereupon the barometric system operates in the normal manner previously described, under control of the barometric contact arm 21.

In the event that the pressure altitude should decrease below a predetermined lower limit (for example. 700

. ""l, tlie arm 151 will engage the opposite side of pin 150 and move sector plate 146 in a clock tsc direction to open the glide switch 143a, 144a and then close the climb switch 145. 143. so that glide clutch 32a wiil be disengaged and climb clutch 32 engaged to move roller 43 to the climb side of its "neutral" position. The altitude arm 151 will then be rotated in the opposite direction, that is. counterclockwise. to permit contact arm 143a to rcccnter the sector plate 146 so that climb clutch 32 is disengaged and glide clutch 32a is rccngagcd. Thus, the barometric system will oscillate about the lower pressure altitude limit until the pressure altitude increases above this limit. whereupon the barometric system will operate in the usual manner previously described.

The circuits between the lmromctric contacts 24. 24a and the control clectromagncts 28. 28.1 of the scrvomcchanism also include an indicated altitude stop limit switch 153. As shown in Fig. 2. the switch 153 comprises lixed contacts 154. 154a connected to the climb conductor 27 and the glide conductor 27H leading from the contact arms I44 and 144a. respectively. of the transfer limit switch 142. The contacts 154 and 1541/ are normally engaged by contact arms 155 and 1551/ connected to conducting blocks 156 and 15611, respectively. which in turn are connected through the conductors 27 and 27a to the respective climb and glidc magnets 28 and 28:1. Mounted on the contact blocks 156 and 15611 are adjacent flexible contact arms 157 and 1570, respectively, normally engaging an intermediate stationary member 158 made of insulating material. The contact arms 157. 1571i and the intermediate insulating member 158 are disposed within a stationary U-shapcd member forming lixcd contacts 159 and 15911 which are normally spaced from and coact with arms 157 and 1570. respectively, the contacts 159 and 159a being grounded, as shown at 61).

An arm 162 is mounted loosely on the indicated altitude shaft 13611 and has an insulating head 163 provided with adjacent slots for closely receiving the free end portions of contact arms 155-157 and 1550-4570, respectively, the slots being separated by an abutment wall 164 disposed between the arms 157' and 157m. A second arm 165 is mounted on shaft 1361! and rotates with it to engage and actuate the insulating head 163.

The shaft 13611, as previously described, rotates in accordance with the indicated altitude, as distinguished from the pressure altitude which governs the rotation of shaft 73. In the event that the indicated altitude exceeds a predetermined upper limit (for example, 20,000 lb). the resulting clockwise rotation of shaft 136i! causes arm 165 to engage the insulating head 163 and move it in a clockwise direction. As a result, the climb switch 154l55 is opened to break the circuit through conductor 27 to the climb magnet 23 and thereby prevent further displacement of roller 43 from its neutral position. The indicated altitude shaft 136:1. however. continues to rotate in the clockwise direction (Fig. 2) through action of the displaced roller 43 and causes the abutment wall 164 on insulating head 163 to engage contact arm 15711 with the grounded contact 159a. whereby a circuit is established from the positive side of current source 30 through conductor 29. glide magnet 28:1. conductor 2711, block 1560, switch 157a1591/, and ground connections and 3011 to the negative side of the current source. The glide magnet 28a is thus energized and engages clutch 32a to move roller 43 to the glide side of its neutral" position, thereby rotating the indicated altitude shaft 136a in the opposite direction, that is counterclockwise.

The spring action of contact arm 155 then returns the insulating head 163 to its normal centered position, opening the glide switch 157a-159a and reclosing the climb switch 154155. The glide clutch 32a is thus disengaged and climb clutch 32 rcengaged to move roller 43 back to the climb side of its neutral" position, so that the indicated altitude shaft 136a is again rotated in a clockwise direction. This operation is repeated to cause the barometric system to oscillate about the upper limit of the indicated altitude, until the latter decreases below the upper limit, whereupon the system operates in the usual manner previously described.

In the event that the indicated altitude decreases below a predetermined lower limit (for example, zero altitude), the arm 165 in its counterclockwise rotation engages the opposite side of insulating head 163 so as to open the glide switch 154a155a and close the climb switch 157--159 to ground. The altitude arm 165 will then be cause the barometric system to oscillate about the lower.

indicated altitude limit.

A VH limit switch 167 is also inserted in the connections 27, 270 between the climb and glide contacts 24, 24a and their respective electromagnets 28, 28a. The switch 167, as shown, comprises a pair of fixed contacts 168 and 168a connected through conductors 27 and 27a to the conducting blocks 156 and 156a, respectively, of the stop limit switch 153. The contacts 168 and 1680 are normally engaged by movable contact arms 169 and 169a, respectively, the free ends of which are disposed on opposite sides of :1 lug 170 mounted on the roller carriage 52. If the actual V1; exceeds the limit in the climb direction (for example, -45 ft. per see.) the resulting movement of carriage 52 moves lug 170 to engage contact arm 16) and thereby open the circuit to the climb magnet 28, thus preventing any increase in the instrument Vrr. Similarly, if the actual Vn exceeds the predetermined limit in the glide direction (for example, +150 ft. per sec.), the resulting movement of roller carriage 52 causes lug 170 to engage the other contact arm 169a to open the circuit to glide magnet 28a, thereby preventing any change in the instrument Vn. When the switch 167 is thus actuated at either Vu limit, the altitudes registered by the instrument on dials 72 (pressure) and 136 (indicated) will lag behind the actual pressure and indicated altitudes as long as the actual Va is greater than the limit of the instrument, and for as long a time thereafter as is required for the altitude dials 72 and 136 to catch up to the actual pressure and indicated altitudes with the maximum Vn in the instrument.

It will be apparent from the foregoing that the altitude limits of the instrument are plus 20,000 ft. indicated altitude or pressure altitude, whichever comes first, and

zero indicated altitude or -700 ft. pressure altitude,

whichever comes first. However, it will be understood that these altitude limits may be varied to suit particular requirements and that the V1: limits set by the switch 167 may likewise be varied. By means of the switches described, any possible damage to the instrument due to operation at extreme limits is effectively prevented.

Operation Before the aircraft takes off, the roller a of the syncbronizing bombsight (Fig. 3) should be offset from its zero position on the axis of speed disc 5, by suitable adjustment of rate knob 50, and the displacement clutch 5] should be disengaged. The control device should then be turned on, as by means of a switch 172 (Fig. 2), and allowed to operate for several minutes before making any adjustments. The altitude setting knob 140 should then be pulled out and turned until the altitude scale 1360 indicates zero or the altitude of the take-elf field above the target, the knob then being returned to reengage gears 112, 112a If the pressure altitude is below the lower limit of the barometric system (700 ft. as described), the scale 136c should not be set at Zero but should be set at the difference between the lower limit of the instrument and the pressure altitude. For example, if the barometric pressure is 30.8" (pressure altitude of 800 ft.) the altitude scale 1360 should be set at +100 ft. The control device should then be turned off at the switch 172.

In preparation for the bombing run, the indicated altitude on scale 1360 must be corrected for deviation from standard temperature, the disc speed correction knob 126 must be set, and the proper trail setting must he made on the bombsight through the trail arm 70. a; previously described. The control device may then be turned on again by switch 172. Since the maximum rate of climb of the instrument is 45 ft. per second, some time will be required for the instrument to read the correct altitude. The bomb release altitude to be used is estimated, and the temperature correction for that altitude is computed by the bombardicr, the amount of the temperature correction being put in through the correction knob with the gears 112 and 11211 disengaged. lf the aircraft is not flying horizontally, the altitude correction should be made with the instrument turned off. Also, if the aircraft is to fiy at an altitude higher than the upper lin-it of the instrument, the altitude correction should be made before it reaches its limit, and the instrument should then be turned off until the altitude is again within the limits. From bombing tables for the type of bomb used, the bombardicr obtains the disc speed correction for the estimated values of altitude, air speed and vertical speed of release. this correction being put into the instrument by turning the disc speed correction knob 12.0. The bombardier also obtains from standard trail tables the trail for the estimated release altitude and air speed and sets this value into the bombsight by trail arm 70.

During the bombing run, the synchronizing bombsight is operated in the usual manner except that it is unnecessary for the bombardicr to adjust the speed of the speed disc 5. Also, in a glide, a fixed rate setting of rate knob 52 will give only momentary synchronism and, therefore, it will be necessary to adjust the rate knob continually during the run.

1 claim:

l. in a synchronizing bombsight having a speed disc, :1 speed disc control device comprising means for measuring the altitude of the bombsight, a driving element for the bombsight speed disc, and a computer connected at its input end to the altitude measuring means and at its output end to the driving element and operable to control the speed of said element in accordance with measurements of said altitude means.

2. in a synchronizing bombsight having a speed disc, at speed disc control device comprising a member movable in accordance with changes in altitude of the bombsight, a second member movable in accordance with the rate of change in altitude of the bombsight, a main computer operatively connected to said members and including an output element and means responsive to movements of said members for transforming said movements into corresponding displaccments of said output element proportional to Where H is altitude and [v is the vacuum time of fall of the bomb from that altitude, a secondary computer operatively connected to said output element and including a secondary output element and means for transforming movements of the first output element into displacements of the secondary output element proportioned to and means operable by the secondary output element for controlling the speed of said disc.

3. A speed disc control device for synchronizing bombsights, which comprises barometric means for measuring altitude and rate ol change of altitude, a speed disc driving element, and a computer operativcly connected between the barometric means and said element and operable to control the speed of said element as a function of said altitude and rate of change of altitude as measured by the barometric means.

4. A speed disc control device for synchronizing bombsights, which comprises barometric means for measuring altitude and rate of change of altitude, a speed disc driving element, a computer operativcly connected between the barometric means and said element and operable to control the speed of said element as a function of said altitude and rate of change of altitude as measured by the barometric means, and safety means for limiting the control effect of said barometric means above a predetermined altitude limit.

5. A speed disc control device for synchronizing bombsights, which comprises barometric means for measuring altitude and rate of change of altitude, a speed disc driving element, a computer operatively connected between the barometric means and said element and operable to control the speed of said element as a function of said altitude and rate of change of altitude as measured by the barometric means, and safety means for limiting the control effect of said barometric means below a predetermined altitude limit.

6. A speed disc control device for synchronizing bombsights, which comprises barometric means for measuring pressure altitude, pressure altitude corrected for variations from standard atmospheric conditions, and rate of change of altitude, a speed disc driving element, a computer operatively connected between the barometric means and the driving element and operable to control the speed of the driving element as a function of said corrected pressure altitude and said rate of change of altitude. and safety means for limiting the control etfect of the barometric means above a predetermined pressure altitude limit or corrected pressure altitude limit, whichever comes first.

7. A speed disc control device for synchronizing bombsights, which comprises barometric means for measuring altitude and rate of change of altitude, a speed disc driving element, a computer operatively connected between the baromctric means and said element and operable to control the speed of said element as a function of said altitude and rate of change of altitude as measured by the barometric means, and safety means for limiting li .151? fl where g is the acceleration of gravity and AS is the correction introduced by said manual means.

9. In a bombsight device of the character described,

a computer comprising an H member movable in accordance with changes in the bombsight altitude, a VH member movable in accordance with the rate of change of the bombsight altitude, a computer slide, a lever pivotally mounted on an axis on the slide and having two elongated guide means extending from said axis at an angle to each other, a fixed stud engaging one of said guide means, a VB slide movable parallel to said first slide and engaging the other of said guide means, a block for guiding the Vrr slide and movable at right angles to the direction of movement of said slides, a driving connection between the V11 member and the VH slide, a driving connection between the H member and the block, a disc speed control element, and means operable by the first slide for producing a motion of said element which is inversely proportional to the movement of said first slide.

10. In a bombsight device of the character described, an H spindle rotatable in accordance with changes in the bombsight altitude, a V1; member rotatable in accordance with the rate of change of the bombsight altitude, a computer slide, a lever pivotally mounted on an axis on the slide and having two elongated guide means extending from said axis at an angle to each other, a fixed stud engaging one of said guide means, a Vrr slide engaging the other of said guide means, a block threaded on the H spindle and movable thereby at right angles to the direction of movement of said slides, the block having means for guiding the movement of the Vrr slide, a driving connection between the VB member and the Vrr slide for moving the Vu slide on said block guiding means i in a direction parallel to the direction of movement of smears: slide, a disc speed control element, and means tit) operable by the first slide for producing a motion of said element which is inversely proportional to the movement of said first slide.

11. In a bombsight device of the character described, a computer comprising an H member movable in accordance with changes in the bombsight altitude, a Vrr member movable in accordance with the rate of change of the bombsight altitude, a computer slide, a lever pivotally mounted on an axis on the slide and having two elongated guide means extending from said axis at an angle to each other, a fixed stud engaging one of said guide means, a Vrr slide movable parallel to said first slide and engaging the other of said guide means, a block for guiding the VB slide and movable at right angles to the direction of movement of said slides, a driving connection between the V1; member and the Vu slide, a driving connection between the H member and the block, a disc speed control element, means operable by the first slide for producing a motion of said element high is inversely proportional to the movement of said llt'fii slide, and correction means for displacing said element independently of said motion producing means.

12. In a bombsight device of the character described, a computer comprising an H member movable in accordance with changes in the bombsight altitude, a VH member movable in accordance with the rate of change of the bombsight altitude, a computer slide, a lever pivotally mounted on an axis on the slide and having two elongated guide means extending from said axis at an angle to each other, a fixed stud engaging one of said guide means, a VB slide movable parallel to said first slide and engaging the other of said guide means, a block for guiding the Vn slide and movable at right angles to the direction of movement of said slides, a driving connection between the Vrr member and the Vr-r slide, a driving connection between the H member and the block. manually operable means for adjusting said last driving connection for altitude corrections, a disc speed control element, means operable by the computer slide for producing a motion of said control element which is inversely proportional to the movement of said first slide, and correction means for displacing said element independently of said motion producing means.

13. In a device of the character described having barometric means including an H member positioned in accordance with changes in altitude, a Vn member positioncd in accordance with the rate of change of altitude, and a constant speed motor for moving said members, a variable speed driving connection between the motor and the H member for positioning the H member and adjusted in accordance with movements of the V1; member, said driving connection comprising a disc rotatable by the motor, a roller engaging one face of the disc and driven thereby at a speed dependent upon the radial position of the roller on the disc, means operatively connecting the roller to the V}: member for positioning the roller radially on the disc in accordance with movements of the Vrr member, a differential mechanism driven at one side by rotation of the roller and at the other side by the constant speed motor, said mechanism having a driven output element which is stationary when the roller is offset from the axis of rotation of the disc a radial distance determined by the drive ratio between the said other side of the differential and the motor, and a driving connection between said output element and the H member.

References Cited in the file of this patent UNITED STATES PATENTS 548,860 Amcs Oct. 29, 1895 578,536 Auriol Mar. 9, 1897 2,116,180 Tomlinson May 3, 1938 2,371,606 Chafee Mar. 20, 1945 2,409,648 Van Auken Oct. 22, 1946 2,410,097 Morgenthaler Oct. 29, 1946 2,431,919 Clark Dec. 2, 1947 2,438,532 Barth Mar. 30, 1948 FOREIGN PATENTS 457,761 Great Britain Nov. 30, 1936 

